project: Fix a integrity violation while deleting.
project: Fix a integrity violation while deleting.

This exception is caused by refering Project from CodeComment.

brainagenet/yobi,naver/yobi,yona-projects/yona,Limseunghwan/oss,yona-projects/yona,doortts/forked-for-history,ChangsungKim/TestRepository01,Limseunghwan/oss,doortts/forked-for-history,bloodybear/yona,ChangsungKim/TestRepository01,violetag/demo,doortts/fork-yobi,doortts/forked-for-history,ihoneymon/yobi,oolso/yobi,yona-projects/yona,doortts/fork-yobi,brainagenet/yobi,ahb0327/yobi,naver/yobi,brainagenet/yobi,bloodybear/yona,oolso/yobi,Limseunghwan/oss,violetag/demo,bloodybear/yona,bloodybear/yona,ahb0327/yobi,ahb0327/yobi,yona-projects/yona,oolso/yobi,doortts/fork-yobi,ihoneymon/yobi,ihoneymon/yobi,doortts/fork-yobi,naver/yobi